The invention relates to radiology instruments, for example, for neurological or vascular use.
A neurology instrument of this type is generally composed:
of an X-ray tube and a collimator for forming and delimiting the X-ray beam, PA1 of an image receiver, generally a radiological image intensifier associated with a video camera, PA1 of a positioner which carries the assembly consisting of the X-ray tube and the collimator, as well as the radiological image intensifier and the video camera, this positioner being capable of moving in space about at least two orthogonal axes, possibly about three axes, and PA1 of a table provided with a plate which is intended to support the patient in a recumbent position.
In the case when the positioner is provided with three axes of rotation, the orientation in space of two axes depends on the angle of rotation about a vertical axis. These angles of rotation are orthogonal towards one another and intersect at a point which is referred to as the isocentre of the positioner. This configuration makes it possible to orientate the axis of the X-ray beam in almost all directions in space. The plate of the table can moved along three orthogonal axes so as to position patient correctly with respect to the isocentre of positioner.
The X-ray tube is powered by a high-voltage generator, and the images output by the video camera are processed, displayed and stored in an image processing system.
A radiological instrument of this type may, in particular, be used for performing interventions using a device which is referred to as a stereotaxy frame. This frame makes it. possible to immobilize the patient's head using four metal points inserted into the cranium in small holes drilled into the bone by the surgeon.
This chassis is associated with a positioning and guiding device so as to intercept the X-radiation with a view to positioning and guiding probes intended to interact with the patient's head, for example probes intended to be introduced into the patient's cranium. At the present time, radiological instruments of this type require special rooms using two high-power sources of X-radiation, arranged orthogonally with respect to one another at a very large distance from the patient, typically at a distance greater than or equal to 5 meters, so as to obtain quasi-parallel radiation at the patient's head.
Once the patient has been positioned, the surgeon injects a contrast product into the vessels of the head and acquires radiological images of the patient's head. The vessels are visible by virtue of the contrast product. The surgeon then arranges, between the chassis and the image receiver, a perforation guide which, in the case in point, is composed of a thick grid, typically 30 mm thick, perforated with about one hundred holes having parallel axes. The surgeon then acquires an image of the grid superposed with the stereotaxy chassis and the patient's head, then by superposing the image containing the opacified vessels and the image containing the grid on a luminous screen, he determines which holes in the grid do not lie opposite vessels. The surgeon can therefore position the probes facing selected holes and use these guide holes to perforate the patient's cranium.
Further to the fact that an instrument of this type has the major drawback of requiring a special room, because of its very large size, the use of a thick grid to locate the position of the probes almost completely masks the internal anatomical structures of the object to be radiographed, in the case in point the patient's head.